Storm surges, perspectives and options

Transcription

1 Storm surges, perspectives and options Katja Woth and Hans von Storch Institute for Coastal Research GKSS Research Center, Geesthacht PAGE 1 Theme 'Natural hazards, sea level rise and coastal erosion', on May

2 Overview 1.Storm surges global phenomenon, with regional manifestation. 2.Midlatitude storminess 3.The case of the German Bight 4.The case of Hamburg assessment and options PAGE 2

3 Overview 1.Storm surges global phenomenon, with regional manifestation. 2.Midlatitude storminess 3.The case of the German Bight 4.The case of Hamburg assessment and options PAGE 3

4 Storm surges are a global phenomenon in regions, where strong storms happen - at mid-latitudes (e.g., North Sea, Baltic Sea, Adriatic, Irish Sea ) - in the tropics where typhoons emerge. PAGE 4

5 Storm Nargis Tropical storms surges: typical spatial scale of storm km; amplitude up to 7-8 m; 200 km coast line affected; several hours up PAGE 5 to half a day (Gönnert et al., 2001)

6 Two scientific tasks: - operational forecasting - determining present risk, present change of risk and possible future risk PAGE 6 Tracks

7 Climate community dealing with recent, present and future storm surge climatology is fragmented. In Europe since WASA and STOWASUS significant progress has been made (see below); in other parts of the world only little; in tropical regions none. The European methodology of dynamical downscaling, originally developed in WASA, is presently exported to other parts of the world. PAGE 7

8 Overview 1.Storm surges global phenomenon, with regional manifestation. 2.Midlatitude storminess 3.The case of the German Bight 4.The case of Hamburg assessment and options PAGE 8

9 In the early 90s, the specter of Global Warming entered the perception of people. Storm got worse Proxy for storm activity in the North Sea region (after Alexandersson, SMHI, 2003) Scientists related worsening of storm climate to GHG emissions (warmer world > more water vapor > more energy for storms > situation will continue to worsening). Insurance companies supported the claims. Media took up the message, which is consistent with cultural preconception of humans changing climate to become worse. Nowadays widely accepted among media and lay-people that storms are getting worse. However, the claim is false. PAGE 9

10 2 1 Proxy for storm activity in the North Sea region (after Alexandersson, SMHI, 2003) Lund; Stockholm Bärring, L. and H. von Storch, 2004: Northern European Storminess since about Geophys. Res. Letters 31, L20202, doi: /2004gl020441, 1-4 PAGE 10

11 Air pressure-based storm proxies for low values less storms NW, N and C Europe Matulla, C., W. Schöner, H. Alexandersson, H. von Storch, and X.L. Wang, 2007: European Storminess: Late 19th Century to Present, Climate Dynamics DOI /s y East Canada Matulla, C., and H. von Storch, 2008: Changes in Eastern Canadian Storminess since submitted high values less storms PAGE 11

12 Overview 1.Storm surges global phenomenon, with regional manifestation. 2.Midlatitude storminess 3.The case of the German Bight 4.The case of Hamburg assessment and options PAGE 12

13 Dynamical downscaling of recent, ongoing and possible future storminess and associated risks Model of North Sea hydrodynamics Global scenario Dynamical Downscaling Joint work with regional authorities. Tide gauge St. Pauli Empirical localization PAGE 13

14 Weisse et al., J. Climate, 2005 Stormcount t T t T Change of # Bft 8/year PAGE 14

15 Case of German Bight Trends 50%iles of annual percentiles of storm surge heights %iles Weisse & Plüß, 2005 PAGE 15

16 Case of German Bight Temporal development of intra-seasonal 99%ile of high tide levels AFTER subtraction of annual mean high tide and mean annual high tide in Esbjerg (Denmark) and Den Helder (The Netherlands) until PAGE 16

17 Case of German Bight Change of regional sea level and of tidal range in the North Sea at most locations, data inhomogenous because of ubiquitous water works in harbours along the coast. One exception is Norderney, where the Forschungsstelle is situated. It shows: a) A monotonous increase of both mean high tide levels, low tide levelks, and of the mean tidal range. b) Sea level rise amount to about 20 cm/100 years without acceleration. Coastal gauges Island gauges H.-D. Niemeyer, Norderney, pers. comm PAGE 17

18 Case of German Bight Recent, ongoing: Natural climate variability in storminess Effect of water water works Mean sea level rise possibly about 2 mm/yr Scenarios of possible future conditions: To the end of 21 st century, strongest westerly winds enhanced by about 10%. Wind/Air pressure induced increase of storm surges: cm. Mean sea level rise unclear, likely larger than global mean sea level. Increase in storm surge heights in 2030 about 20 cm, in 2085 about 60 PAGE 18

19 PAGE 19 SRES Scenarios SRES = IPCC Special Report on Emissions Scenarios

20 A2 - CTL: changes in 99 % - iles of wind speed (6 hourly, DJF): west wind sector selected (247.5 to deg) HIRHAM RCAO Scenarios for 2085 PAGE 20

21 Localisation : From the 10 m line to the shore Change of winter 99.5%ile of wind and air pressure related water levels (6 hourly data) Δ wind effect, 99.5%-ile [m], Ensemble A2, B2 SRES Dagebüll Husum Δ wind effect, 99.5%-ile [cm] +increase MSL low_res high_res max low_res + ca. 10 % high_res mean min Assumed increase in MSL: 30 cm Estimated with a regression model, trained with high resolution hindcast. PAGE 21

22 Overview 1.Storm surges global phenomenon, with regional manifestation. 2.Midlatitude storminess 3.The case of the German Bight 4.The case of Hamburg assessment and options PAGE 22

23 Localisation : From the coast into the estuary St Pauli Cuxhaven PAGE 23

24 Only the effect of anthropogenic climate change (A2, B2) - No effect of water works. Scenarios 2030, 2085 PAGE 24

25 PAGE 25 Hamburg storm surges

26 Hamburg storm surges Where does the enhanced storm surge levels Hamburg come from? Sea level rise a few centimeters Intensification of storm activity What else has happened in the coastal/estuarine environment? PAGE 26

27 Difference in storm surge heights mouth of Elbe estuary and Hamburg, The tidal change is due to coastal protection measures and modifications of the tributaries, and to the deepening of the shipping channel. These measure also had an effect on the heights of severe storm surges estimates are 45 cm caused by measures of coastal defense and 15 cm by deepening the shipping channel (Haake, 2004: 27). PAGE 27

28 Options for dealing with future elevated storm surge levels - at the coast: + fortifying, extending presently installed coastal defence + flexible response strategies; + design dykes such that the amount of water which may safely spill over for a few hours, is considerably larger than allowed today. -in the estuary: partial undoing of previous man-made increases PAGE 28

29 Dyke overtopping tolerance Currently overtopping tolerances: 3% of all Lower Saxony 2 l/(m s) Masterplan Schleswig-Holstein 0,1-1,0 l/(m s) The Netherlands Results of overtopping test in Delfzijl/NL No damage up to 50 l / (m s) No severe damage at 50 l (m s) after artificial damage still functioning PAGE 29 Niemeyer & Kaiser 2008, NLWKN

30 Dealing with rising sea level and elevated storm surge heights in Hamburg 1. Additional flooding areas The Tidal Elbe concept of Hamburg Port Authority 2. Availability of additional polders to be flooded during severe storm surges to cap the peaks of such surges. 3. Additional dissipation of tidal (and surge) energy by narrowing the mouth segment of the estuary PAGE 30 Heinz Glindemann, HPA, pers. comm.

31 Conclusions Storm surges are a serious issue Storm surges are an interesting issue. We have developed a methodology to characterize recent, ongoing and possible future storm surge conditions - by analyzing air-pressure proxies available for the 20 th century and longer, and - by running a cascade of global/regional/impact models The North Sea is the best studied area, with no indications for present man-made change but perspectives for increases of 20 cm and 70 cm in 2030 and 2085 in its SE storm surges. These numbers are uncertain and represent scenarios. PAGE 31

32 Conclusions Most of the increase will take place even if the ambitious climate control measures will be successful. Thus the preparation of adaptive mearues are needed. Novel adaptive measures need to be developed and examined, e.g., - damping of incoming tidal energy in estuaries - improving dyke design to allow for stronger overtopping. The same type of studies need to be implemented in tropical regions. PAGE 32